Action film parody “Tropic Thunder” clung to the top spot at the North American box office for a third straight week as the summer moviegoing season sputtered to a lackluster close, Hollywood studios reported on Sunday.

Paramount Pictures’ farcical combat movie within a comedy, starring Ben Stiller, Robert Downey Jr. and Jack Black, sold an estimated $11.5 million in U.S. and Canadian tickets Friday through Sunday to bring its three-week tally to $83.8 million.

While the final weekend heading into the U.S. Labor Day holiday is typically one of the slowest of the summer, the box office was especially lethargic despite five new films competing for attention in domestic theaters. None of those even managed to even crack the $10 million mark.

“It was an underwhelming end to a phenomenal summer,” said Paul Dergarabedian, head of box office tracking service Media By Numbers.

Business also was likely dampened by the approach of Hurricane Gustav along the U.S. Gulf Coast, where many families were too busy boarding up their homes and fleeing to higher ground to go to the movies.

“Tropic Thunder,” about a group of self-absorbed actors who get caught up in a real-life battle with narco-terrorists while filming a war movie in Southeast Asia, was the only film to post ticket sales in the double-digit millions.

Its biggest competition came from a real action flick, the sci-fi thriller “Babylon A.D.” from 20th Century Fox starring Vin Diesel, which grossed an estimated $9.7 million in its first weekend to land at No. 2.

Blockbuster Batman sequel “The Dark Knight” climbed up a notch on the box office chart to No. 3 with weekend receipts of nearly $8.8 million, pushing its cumulative domestic haul to an estimated $502 million after 45 days in release.

“Dark Knight,” a Warner Bros picture, becomes only the second film to cross the $500 million threshold. Two weeks ago, it surpassed “Star Wars” as the second highest grossing movie ever, behind only “Titanic” at $601 million.

Weekend ticket sales as a whole were sluggish, however, down 14 percent from the same period a year ago, as several new films failed to gain traction at the megaplex.

Two comedies opening on Friday, “Disaster Movie” and “College,” plus Don Cheadle’s thriller “Traitor,” which debuted on Wednesday, and “Hamlet 2,” a comedy that expanded nationally on Wednesday, grossed just $17.9 combined this weekend.

Together with “Babylon A.D.” those films together accounted for $27.6 million in ticket sales, only about $1 million more than the top-grossing movie from last year’s same weekend, “Halloween,” managed all by itself.

The Labor Day holiday on Monday marks the official conclusion to the 18-week summer film season, which can account for as much as 40 percent of the movie industry’s total business for the year.

When final studio figures come in later this week, Hollywood is expected to eke out roughly $4 billion in North American box office receipts, perhaps even slightly exceeding last summer’s record $4.18 total.

But with the actual number of admissions down more than 3 percent from a year ago, the gain in revenues is fueled mostly by higher ticket prices.